1. Field of the Invention
The present invention relates to a stage device and a stage cleaning method. In particular, the present invention relates to a stage device having a function of efficiently cleaning a track surface of a sample stage using an air bearing in a vacuum in an electron beam exposure system or the like, and a method of cleaning a stage of the same.
2. Description of the Prior Art
In electron beam exposure systems and electron microscopes, a sample is exposed, observed, or measured while being mounted on a stage. For example, an electron beam exposure system performs exposure while moving a stage in accordance with exposure data so that a required position on a wafer may be exposed.
Such stages include cross roller bearing stages. In cross roller bearing stages, rollers in a track between a movable stage and a fixed stage revolve to move the movable stage. When such stages are in use, oil for vacuum devices is applied to a track and rollers for the lubrication of the track and the prevention of particle generation.
When such a stage with a mechanical bearing is used in a state where a particle exists on a track, the particle causes strain in the stage mechanism. Such strain degrades the operation of stage position detection, and makes it difficult to detect a stage position accurately. A particle does not remain at a certain place on the track but moves as the stage moves. This phenomenon hinders replication of the position change of the stage and prediction of a position to which the stage is moved. Thus, the stage mechanism has difficulty in correcting the position of the stage. Further, in the case where oil is applied to the track, particles can be removed to a certain extent while the oil exists, but the amount of particles may rapidly increase when the oil is lost.
In contrast to such stages using mechanical bearings, technologies using air bearings have been studied and used. For example, Japanese Patent Application No.2006-66589 describes a stage device in an exposure system for use in photolithography. In the stage device, a movable member is supported on a base member in a noncontact manner using a fluid bearing (gas bearing or air bearing).
When such an air bearing is used, the degradation of accuracy of a stage caused by particles on the track of the stage can be reduced compared to when a mechanical bearing is used.
However, the stage device is not necessarily always able to prevent degradation of accuracy of the stage for any-sized particles. For example, in the case where there is a particle of a size approximately equal to the height of the noncontact portion, the particle may be entangled when the stage is moved, and the fixed member and the movable member may come into contact with each other. When such a situation arises, the attitude of the stage mounted on the movable member becomes unstable. This results in accuracy degradation.
It should be noted that no techniques have been reported for removing particles in the case where a stage is moved using an air bearing mechanism in a vacuum.